module Daemon (background) where

import Config
import Control.Monad
import System.Exit
import System.IO
import System.Posix

background :: Option -> IO () -> IO ()
background opt svr = do
    putStrLn $ "Serving on port " ++ show port ++ " and detaching this terminal..."
    putStrLn $ "(If errors occur, they will be written in \"" ++ opt_report_file opt ++ "\".)"
    hFlush stdout
    daemonize svr
  where
    port = opt_port opt

daemonize :: IO () -> IO ()
daemonize program = ensureDetachTerminalCanWork $ do
    detachTerminal
    ensureNeverAttachTerminal $ do
        changeWorkingDirectory "/"
        void $ setFileCreationMask 0
        mapM_ closeFd [stdInput, stdOutput, stdError]
        program
  where
    ensureDetachTerminalCanWork p = do
        void $ forkProcess p
        exitSuccess
    ensureNeverAttachTerminal p = do
        void $ forkProcess p
        exitSuccess
    detachTerminal = void createSession